text:
If an A/C have Radio failure ( sqk 7600 ) How the ATC will give him instruction or how will he land?
If an A/C have Radio failure ( sqk 7600 )
How the ATC will give him instruction or how will he land ?!

This is a question with many answers, depending on the conditions of the flight. Let me limit myself to private recreational aviation (what the FAA calls Part 91) in a single-engined propeller aircraft.
If you are flying Visual Flight Rules (VFR), there are some airspaces you need to stay out of. For instance, US and Canadian Class B and C airspaces require radio communication. You won't be able to land at airports in such airspaces without some other arrangements.
You can give a signal that you are lacking radio communication. Squawking 7600 on your transponder is one way. Flying a triangular pattern, which might be visible to ATC on radar, is another way. I have sometimes used my cell phone to call ATC's phone number.
Control towers in the US and Canada might well have "light guns": bright spotlights which the controller can point at an aircraft, and colour red or green, and shine continuous or blinking light. A continuous green light from tower to an aircraft preparing to land means that aircraft is cleared to land.
If you are flying Instrument Flight Rules (IFR), there are specific procedures to follow if you are unable to communicate with ATC.  Frequently they boil down to holding for a few minutes, then continuing on your flight planned route.
Remember that some aircraft have no electrical system, let alone radios. They fly, take off, and land just fine. There are many airfields with no control towers. There is uncontrolled airspace in which to fly. In these cases, pilots maintain safety by seeing and avoiding other aircraft. Pilots fly traffic patterns before landing, and sequence themselves cooperatively.  Lots of aviation works just fine without radio communication between pilots and ATC.

This also depends on the nature of the failure: If you can still receive but not transmit ATC will frequently ask you to acknowledge instructions by using the IDENT function on your transponder. This lets them know that you can still receive their instructions and they can direct you someplace where you won't be a problem.

Many thanks for you .

Good answer - I think the IFR comment is the relevant one here - you squawk 7600 for long enough for the ATC to notice you and get everyone out of your way... then you continue as planned and land, trusting ATC to deal with things. That's essentially the point of the 7600 code - to flat your situation up to ATC and let them deal with it. If you declared an emergency then they'd clear traffic out of your way anyway, and "We don't know where we're meant to be!" is somewhat urgent...


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What is the diffference between landing lights, taxi lights and external lights?
A comment on this website along with an answer for the same question added confusion to my mind. Before reading this, I thought taxi lights and landing lights were the same, which seems to be true is some cases. I thought those lights were used for approach, taxiing, and take off and were strong lights designed to light the floor in front of the aircraft in the darkest night. Moreover, the answer linked above speaks of exterior lighting.
Now, I got a serie of questions to clarify the role of those "exterior lighting":

What are the difference between them (landing lights, taxi lights, other exterior lights I never heard of)?
What purpose do they serve and when are they used? (Perhaps it is the same question)
Are all aircrafts equipped with?

Also for landing lights, and external lights.

There are basically two types of (exterior) lights in an aircraft- the navigational lights, which are required to be switched on from sunset until sunrise and other forms of exterior lights, which can be switched off at the pilot or operated only at some parts of the aircraft operation, like the landing/taxi lights.
A (non-exhaustive) list of aircraft lights:

Navigation lights All aircraft are equipped with a steady light near the leading edge of each wingtip. The starboard light is green while that on the port wing is red. The different colors make it possible for an outside observer, such as the pilot of another aircraft, to determine which direction the plane is flying. These are required to be on during operation (in night).
Navigation or Position lights In addition to the red and green lights, most large planes like airliners are also fitted with other steady white navigation lights in various locations like the trailing edges of each wingtip, horizontal tail and top of the vertical tail. The main purpose is to increase the visibility of aircraft from behind.
Anti-Collision Beacon lights These are are flashing (or strobe) light assemblies installed on the upper and lower fuselage of aircraft,used to improve visibility of the aircraft. These can be switched off at the discretion of the pilot under some conditions.
Strobe lights High-intensity strobe lights that flash a white-colored light are located on each wingtip. These flashing lights are very bright and intended to attract attention during flight. They are sometimes also used on the runway and during taxi to make the plane more conspicuous.
Logo lights These steady white lights on the surface of or at the tips of the horizontal stabilizer are used to illuminate the company's logo painted on the vertical tail. These are usually switched off in airports to improve the visibility of the aircraft.

1) Navigation lights 2) Aft light 3) Anti-collision strobe lights 4) Logo light
"Jet-liner's lights 1 N" by CC BY 3.0 via Commons.

Wing lights Many airliners feature lights along the root of the wing leading edge that can be used to illuminate the wing and engine pylons in flight. These lights may be used to make the plane more visible during takeoff and landing or to inspect the wings for damage in flight. Pilots can also use the wing lights to inspect the wings and slats for any ice accretion that might build up when flying through clouds.
Taxi lights A bright white lamp is located on the nose landing gear strut of most planes. This light is typically turned on whenever the aircraft is in motion on the ground for greater visibility during taxi, takeoff, and landing.
Landing lights Typically the brightest light in the aircraft, these are fitted on most planes (and helicopters) for enhanced visibility during the landing approach. These lights can also be used to illuminate the runway at poorly lit airports. They can be located in the wing root, in the outboard wing, or somewhere along the forward fuselage (the usual location incase of helicopters), with some aircraft having them in more than one location.

Boeing 787 Lights; Source: captalk.net

Runway Turnoff lights Usually located in the leading edge of the wing root, these bright white lamps are intended to provide side and forward lighting during taxi and when turning off the runway. These lights are most useful at poorly lit airports but are usually unnecessary. The lights can also be used in flight if greater visibility is required.
Wheel Well lights Some planes are equipped with additional lights in the nose and main gear wheel wells. These lights are provided primarily to assist ground personnel in making pre-flight inspections of a plane at night.

The image below shows the lights in a Boeing 737.

Image from staticflickr.com

Landing light
Typically the brightest light on an aircraft. It is like a giant headlight, illuminating the front.
Taxi light
Also a headlight, but not as strong as landing light.
Logo light / Wing light
These lights illuminate the wing or vertical tail surface of an aircraft.

Landing light is very, very bright. You turn it on when you want to see what's in front of the aircraft, or you want everybody to notice you. On a clear night you can easily spot an aircraft heading towards you with its landing light some 10 miles away. When you enter a runway, you turn on the landing lights as a way to shout "I'm here. Don't collide on me" to everybody. If every pilot turns on the landing light at the gate, some ground crews will sure get blinded sooner or later.
If you're on a runway, turn on everything.
If you're on a taxiway, turn off your landing light but keep your taxi light on. Lights like logo & wing light are optional.

Many aircrafts, especially the smaller ones, do not have wing lights. Some aircraft use the same light as landing & taxi light, in which case you should turn it on during taxi as well unless you want to taxi in the dark.

The difference between taxi and landing lights is similar to low and high beam lights in car. Landing lights are much brighter, which is needed to give sufficient visibility during high-speed take-off and landing roll and to make the plane visible from several miles away when in flight, but they would be blinding when used on the apron, so less powerful taxi lights are used when taxiing.
Ultra-light aircraft may not be equipped with any lights at all, so not all aircraft have them, but all aircraft that may be operated at night do. Small aircraft (like Cessna 172) often have the taxi and landing light installed together under one cover, but in most cases there are still two bulbs with different brightness.

source: Stack Exchange

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How is the pushback tug connected to the airliner?
If I understand correctly, there are two way to connect a tug: with or without a bar; and the tug can push back or pull forward the airliner.

When using a bar, how is the tug connected to the airliner? Is there a standardized fixation? Is there any articulation on both sides of the bar?
When using a towbarless tug, the tug lift the nose wheel. How is it done? Is there limitation on nose-wheel dimensions?

You're correct that there are two ways to connect the tug with an aircraft.

In case a tow bar is used, it is fixed laterally at the nose landing gear, while allowing slight movement for height adjustment. Usually, the tow bar may pivot freely laterally and vertically at the end that attaches to the tug rather than the aircraft end, which is fixed. The following image shows the tow bar attachment point in Airbus A380.

Image from alamy.com.

The attachment points differ from aircraft to aircraft, so the tow bar basically operates as an adapter between the aircraft and the tug.

"Pins for pushback". Licensed under Public Domain via Commons.
When using a towbarless tug, the nose wheel is simply scooped off the ground using hydraulic (for large aircraft) or electric power. The tug has a movable arm, which is opened and the tug is moved and placed so that the nose wheel fits inside the fixed arms of the tug. The movable arm is then closed. The movable arm and the opposite side has sloping edges, over which the wheels slide and the nose is lifted off as the arm closes due to hydraulic power.
This video shows how its done in case of Airbus A380.

Video from Youtube: How to lift up the world's largest commercial aircraft the Airbus A380. by user Kasavubu
The nose wheel dimensions and aircraft weight do matter and tugs are certified for different ramp weights.

As mentioned there are two ways used for pushback: towbar and towbarless (TBL) push trucks.
There is a third way that is not as common: the Power Push Unit (PPU).

Source: airliners.net
Unlike the standard pushback process that uses a pushback truck and a towbar attached to the nose wheel, the PPU is a remote controlled truck directly attached to one of the main landing gear bogies. It pushes the aircraft backwards and the pilot steers the nose wheel based on the instructions of the PPU operator.
Based on one company, the way it works is via "pressure rollers [that] grip the tyres. Rotational friction forces drive the aircraft's wheels."

The braless pish truck, every pilot's wet dream! Love it

You should add pictures and references/links to improve your answer.

Still i dont know how to add photos

paste in links, @Hmb, and someone will post them for you. Or, click the little "Image" icon (6th from the left) and it will walk you through the process.

Video: https://youtu.be/1KyT02nqaus

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What is this pattern on the windshield of aircraft?
The image is extracted from this Airbus A350 video (at 3m40s, when taking off)
I circled in purple the strange pattern formed by few black straight lines. I'm quite puzzled as I have no idea of what it is or what purpose it can serve.
EDIT: I would like to sum up the ideas in comments as there is interesting guess and discussions in the comments. It is a strange device which can be:

a kind of gauge useful as the windscreen seems to be a completely new one and the aircraft presented is one of the test aircraft
part of some windscreen heating device

looks like electric windscreen heat to me, but I'll defer to someone with specific systems knowledge of this airplane.

@casey I would concur if it was not placed there. it cover only a small part of the windscreen.

@ManuH It doesn't need to cover more area.  I don't know the a350 but it is almost identical to other screen heaters I've seen.  Those things get really hot, they will burn you hand, and the windscreen only needs to be a little above freezing.

@Simon Ah, so you don't need to be an SR-71 pilot to be able to warm your lunch on the windshield! (As long as you choose the right part of it.)

Darn, I was really hoping it was the cockpit glass detonation cord for the A350 ejection seat. :-)

They look like strain gauges to me. Probably to ensure the windows are within the expected force limits.

@tl8 you may be right. The video shows a test airplane, and I can't find those lines in other videos.

@casey I agree with you.  They are not heating elements as some others have suggested, but rather an electrical bus which provides electricity to a conductive windshield which heats the entire thing.  I'm not familiar with the specific aircraft, but there are three sets, which probably are for something like high, low, and emergency settings for the windshield heat.

I agree with @tl8. The lower (and middle) structure also shows white lines, which look like transparent tape to fix that... device to the screen. As said, it's a test plane, and to my knowledge, the wind shields are new, too.

May be it is shallow

This wiki commons cockpit view shows  the same wires, albeit only 1 set. not 3.

Short answer
These are the three redundant temperature sensors for the windscreen anti icing and defogging system. The design is similar to what is found on the A330 and A340, and most large aircraft. The sensors are used to control the electric current in the heating film(s) sandwiched in the windscreen ply. Usually three temperatures are monitored:

Outer windscreen layer must be above freezing point, e.g. 1.8°C.
Film mustn't overheat, depends on film used.
Inner layer must be below some threshold, e.g. 50°C.

This video shows how windscreen heating works on an ATR42. Extract related to the sensors:

ATR42 windscreen temperature sensors and film bus bars
The heating film(s) is/are used both to prevent icing and failure of the outer panel (air temperature can be as low as -60°C) and fogging on the inner panel. This can be obtain using a single film, but sometimes there are two distinct films:

Structure of the windscreen on a Boeing 787. Source

On the A350
From A-350 Technical Training Manual:

Windows Anti Icing/Defogging Function, Description and Interfaces
The windows anti icing/defogging system is divided into two
sub-systems (F/O and CAPT). Each sub-system is comprised of one
windshield, one FWD lateral window, one AFT lateral window and a
Window Heat Computer (WHC). [...]
The anti icing and defogging function of the cockpit
windshields is ensured by the heating of one resistive/heating ﬁlm. Each
windshield's resistive heating ﬁlm is powered by 230 VAC, provided by
the WHC.
There are three temperature sensors near the heating ﬁlm that
continually send information to the WHC for the heating regulation and
the overheat protection functions. [...]
The WHC regulates the temperature of the cockpit windows (35 degrees C to
42 degrees C) based on the temperature value it receives from one of the three temperature sensors. The other two temperature sensors are
in standby mode. [...]
If the temperature of the cockpit windows reaches a specific
temperature level (+60 degrees C), the WHC will stop supplying the
specific window. [...] For each window, the WHC uses temperature
values from the three temperature sensors to detect an overheat.
The WHCs interface and exchange data via CRDCs with the
AFDX network.The two WHCs are located in the cockpit: WHC1 is located
next to the fourth occupant console behind the Captain. WHC2 is
located next to the coat stowage behind the First Ofﬁcer.

For this test aircraft:

Sensors are larger than usual.
They may be stuck on the glass instead of being built-in.

This setting might be specific for flight test purposes. Someone may bring additional elements.

Another example, on a Pilatus PC12-NG:

Pilatus PC12-NG temperature sensors and bus bars on the windscreen

The inner layer must also be above ambient temperature inside cockpit to prevent the fogging (or at least above dew point, but that's not known).

@JanHudec: True, but with a cabin RH of 20% at 20°C, the dew point is below 0°C. So that would be a problem only prior to closing the doors.

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Are the fastest moving pieces of a jet engine supersonic?
A jet engine is composed of fast moving pieces. Those pieces are moving into an airmass different form the ambient airmass the aircraft is flying into.
The turbine pieces are spinning quite fast, thus its blade tips may be moving at a supersonic speed. But, the airmass may also be spinning modifying the speed of the blades into the airmass. Moreover, the temperature of the air at this stage may modify the speed of sound.
The first stage of compressor is spinning at a much familiar air temperature and pressure, thus it may be easier to find if those compressor's blades' tips are moving faster than the speed of sound. But pressure (and thus temperature) is not the same before and after each compressor stage. It may be hard to define the speed of sound for this airmass going through the compressor.
Given the airmass inside a jet-engine is different from the ambient airmass, are there any moving piece inside a jet-engine whose velocity (frame of reference: the airmass in which it is moving) is greater than the speed of sound?

Yes, the tips of the fan blades.
Let's look at an example: The GE-90 has a fan diameter of 3124 mm and a maximum rotational speed of 2475 RPM. Their circumferential velocity is d·π·41.25 = 405 m/s or Mach 1.19 at sea level and ISO atmosphere. Now you need to add the flow speed of the air, but this calculation alone should be sufficient to prove the point.
The inner part of the fan and all the compressor stages belonging to the core engine experience flow at subsonic speed, even if the whole engine is flying at supersonic speed (see picture below). To make ignition as complete as possible, the flow speed is continuously reduced the closer you move to the fuel injectors. Since the air is heated in the combustion chamber, the hotter gas has a higher speed of sound, and all the flow through the turbine is subsonic, too. This includes the low-pressure turbine. Even the 1,600 ft/s shown below at the turbine is subsonic, because at 1100°C the speed of sound in air is 720 m/s or 2,362 ft/s.

Overview of parameters in a typical jet engine.
Only in the rear part of a convergent-divergent nozzle with reheat switched on will supersonic flow again be attained. This is exactly aft of the narrowest section, called the throat, where airspeed is equal to the speed of sound, and the petals of the nozzle are the only moving parts here. And they move rather slowly.

Does that mean there is a sonic boom every time you turn on the engine? If so, why dont we hear it? Is it just small/muffled by everything else?

@DavidGrinberg: A combination of this answer and this answer should help: Yes, those tips make a lot of noise, but the engine shroud helps to keep it manageable.

@DavidGrinberg Keep in mind that a sonic boom isn't produced when going from subsonic to supersonic ('breaking the sound barrier'), but is rather a continuous shock wave produced by objects going faster than the speed of sound. It's the loud whirring you hear when taking off in certain jetliners.

I just wanted to add that flow through the Stage 1 High Pressure Turbine (HPT) Nozzles (Vanes) is typically choked (i.e. Mach = 1). Of course, this is only the airflow, not any moving parts. One thing that would make the chart better is if it showed the M=1 line throughout the engine, since speed of sound is proportional to temperature, the speed of sound is much higher in the HPT than at standard sea level.

Just noticed that your image could use some attribution, if you recall where it came from. (It's only been about 8 months...)

@FreeMan: I know - I have it a bit longer and didn't keep a record from where it came.

The wiki page you linked to states 3.1 m fan diameter and 2261.5 rpm. That  equates to 367 m/s, or M = 1.07

@Koyovis: Thanks for pointing that out! I used the figures from the Stanford report but misread the maximum RPM. Corrected, but with a slightly higher result. The maximum permissible speed is a few percentage points above 100%, which is probably what Wikipedia uses.

In a turbofan engine, the fastest moving parts are usually the bypass fan tips. This is because at the same rotational speeds, the outer tips are at more distance and have higher linear velocities. In some engines, the tips reach supersonic speeds, usually at high thrust conditions. This is the reason for having a swept blade (like swept wing) in high bypass turbofans.

Source: sheffield.ac.uk
In case of turbine blades (and to a lesser extent, compressors), the local temperature is high (due to combustion and compression); this increases the speed of sound (as it is proportional to $\sqrt{T}$ for an ideal gas). Due to this effect, the local flow is subsonic. Also, the blade size is very small compared to the bypass fan.
The next part where the flow goes supersonic is the divergent section of the convergent-divergent nozzle used in military jets (Note that there are no moving parts here).

It may be true that the bypass fan blade tips are fastest, but your answer does not offer supporting evidence. If N1 is sufficiently below N2, other blade tips might exceed the bypass fan blade tips.


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Why do we use pylons to mount the engines on jetliners?
This question focus on jet airliners.
The De Havilland Comet's engine were mounted inside the wing, the Concorde's engines were mounted underwing (as many jet engines) but without pylon. It seems jet airliners' engines are now mounted on pylon. That assumption goes wherever the engine is mounted (underwing or at the rear of the aircraft).
What are the advantages of doing so (aerodynamic, maintenance, safety,...)? Is there some drawback (must be minimal as this design is dominant)?
Note: I don't want discussion about where to mount engine (underwing as for the B747, overwing as for the VFW-Fokker 614, at the rear as for the MD-80, ...), I'm curious about why we use pylons for all this designs.

possible duplicate of Why not mount airliner jet engines above the wings?

@GdD It isn't. The answer of the linked question discuss the location of engine, not the fact that we use pylons. The word "pylon" is used only 2 times, both discuting mounting engine over the wing (nothing about pylons itself).

I'd say the answers in there together give all the information you need, however if others disagree I'm sure you'll get explicit answers here.

@GdD I still disagree (otherwise, I wouldn't have ask this question). No answser discuss the absence of pylon (espacially on the 2 aircraft I cite, Comet and Concorde), but only the position of the engine (underwing, overwing or at the rear). I'll edit the question to make it more clear.

I think it's a good question. I'm sure there are many aerodynamic reasons, but I'm guessing it's also related to engine failures. Sioux City happened due to an uncontained engine failure in the tail of the DC11 severing all hydraulic lines of all three systems. Furthermore, the pylon offers an opportunity for the engine to break away cleanly rather than taking the wing with it. Although such attempts have been unsuccessful in the past (e.g. El Al 1862, AA191), it could potentially allow the plane to continue fly.

The main reason not to have the engines inside the body is ease of replacement and maintenance.  With underslung engines on pylons, you just open the covers and do what's needed.  A change is disconnect the control runs and pipes, unbolt the pylon and drop it.

In addition to all the other reasons given here, a fire in an internally-mounted engine is a more serious matter, on account of the increased risk of it spreading to other vital systems or the cabin, or of weakening the wing spar or other vital structures.

Engine placement was a tricky question when jets were introduced, and much has been learned since then. The initial idea was to mount them inside the fuselage or wing root. When they grew too big, they were closely mounted to the wing ("underslung" position, like in the Me-262, the Il-28 or the early Boeing 737).
However, the underslung position has two disadvantages:

More of the leading and trailing edges is obstructed, blocking space that would otherwise be used for slats and flaps. Consequently, an underslung position reduces maximum lift.
The center of gravity of the engine is too far back. Moving it more forward helps to place the center of gravity of the wing ahead of its elastic line. Bending will now create an opposing inertial moment, which is very helpful to dampen flutter.

Starting to move the engine downwards away from the wing initially increases drag, because now a narrow slot opens between both with a tendency to separated flow. Only when the engine is moved downwards enough, the drag of the wing-engine arrangement reaches its minimum. This placement was chosen in the next generation of jets like the B-52 or the Boeing 707.
Moving it still further down makes the pylon longer and thus increases the total drag again.
The big diameters of modern high-bypass ratio engines make it impractical to move it down enough to reach the drag minimum, but by moving it forward, the engine can again be lifted up, so a shorter landing gear becomes possible. Vortex generators are added if that pesky separation between engine and nacelle cannot be avoided.

If over the years we learned underslung wasn't the best, why did Boeing go from more separation on the 707 to less on the 737 (which came after)?

@cpast: Because the initial design was with small JT8D engines and then the low landing gear forced them to put the engine high enough. Covered also here.

I remember reading somewhere that the forwards placement helps with bending loads on the wing, since then the torque from the thrust and the engine weight cancel each other out. Can't find a source for it right now, though, but it makes sense on paper.

@sanchises: The bending relief comes from placing the engines out at the wing. Their mass directly counters lift, regardless of their lengthwise position. Torque from thrust would cause a torsion moment, not a bending moment in the wing. Now this torsional moment does indeed run counter to the torsional moment from the engine mass, but would be rather variable over a whole flight.

@PeterKämpf Sorry, I indeed meant torsion relief. My bad!

Mounting the engine on a pylon rather than integral to the wing, allows the aircraft to accept different engine types (eg, Rolls Royce, P&W, or GE) or different sizes of engines. For example the 757 had three different engines, each made by a different manufacturer:

Launch customers Eastern Air Lines and British Airways selected the
  RB211-535C turbofan built by Rolls-Royce, which was capable of 37,400
  pounds-force (166 kN) of thrust.[19] This marked the first time that a
  Boeing airliner was launched with engines produced outside the U.S.[8]
  Domestic manufacturer Pratt & Whitney subsequently offered the 38,200
  pounds-force (170 kN) thrust PW2037,[19] which Delta Air Lines
  launched with an order for 60 aircraft in November 1980.[8][20]
  General Electric also offered its CF6-32 engine early in the program,
  but eventually abandoned its involvement due to insufficient
  demand.

The pylon not only mounts the engine, but allows the different engine designs to adapt to the airframe.
Secondly, by disassociating the airframe from the engine, the engine can be repaired and replaced without disassembling the wing.

The passenger jet engine mounts (pylons) are designed to break away due to excessive vibration (a type of engine failure) because you would rather drop an engine than have your wing break off and drop like a brick.

Could you expand your answer (direction and intensity of vibration at which the engine is dropped) and add references?

Things were edited out, I have been trying to find the original designer of the concept.

The foremost reason is, the engine is isolated from critical structural components in the wing, enhancing safety. If there were a fire, the fire would not be likely to burn the wing off since the airstream would ensure the flames avoided the wing, in which the fuel is housed in modern jet designs. Also, if the engine were to explode in an uncontained failure, the shrapnel would be less likely to ignite a fuel source, damage a wing spar, or damage flight control surfaces. The hanging pod design surrounding the compressor and turbine sections helps contain catastrophic failures, and the pod design also enables bypass air to envelop the engine on all sides, an important enhancement for hot-section cooling and fuel economy. Additionally, a pylon-mounted engine does not interfere with the airflow over and under the wing to the same degree as a wing-integral design would. Another less important advantage is, the engine is more accessible for maintenance purposes. But a disadvantage is the engine is more vulnerable to picking up foreign object damage, being closer to the ground.

The real answer: pylons make engine maintenance easier and are a more practical solution for current high bypass turbofan engines.

References and links to support your answer and to provide further reading would be welcome to improve your (tiny) answer.


text:
Can you get sucked out of a hole in an aircraft?
I had always been under the impression that the forces of air rushing out a broken window or hole in an airplane would be pretty limited and nothing near the levels necessary to carry a body through to the outside. The scene in Goldfinger has always been scoffed at by other pilots I have known.
However, recently I discovered that allegedly the pilot of an airliner was sucked out of a cockpit window in 1990 (re-enactment photo below):

Seems fishy to me. Is this for real? Can you really be sucked out of an aircraft window? Remind me to buckle up. Gives a whole new meaning to the word "deplaning".

That's like answering your own question. You can be sucked out of the plane because it is pressurized.

Related: 5 Myths About Flying Everyone Believes --- and --- Can We Get Sucked Out of Airplanes? In case of explosive decompression, the main threat seems to be blocking air in lungs, albeit several accidents have led to people being sucked out.

If the hole is big enough, why not? But better think of it as being blown out of the aircraft. That is what really happens. The most unrealistic part of the scene in "Goldfinger" is the duration of the incident - normally, a depressurisation is a very short but violent event.

If the difference between the cabin pressure and the external pressure is say 8 psi (which is the right order of magnitude for cruising at 40,000 ft) it is simple arithmetic to show that is equivalent to a pressure of about half a ton per square foot. That's more than enough to move a human out of his/her seat!

@alephzero: That's the pressure difference you'd experience if you were to wedge yourself into a man-shaped hole in the wall. Otherwise, the air would rapidly move around you, equalising the pressure on both sides of your body. Simple arithmetic gives an upper bound, but the forces acting on someone in his seat can be much smaller.

@MarcksThomas Actually, if you got wedged in such a hole, you'd briefly experience much more pressure than that.

Big difference here, in that the hole that pilot is being sucked (blown) out through is the entire front windshield of the plane.  In Goldfinger, the guy gets sucked out through a bullet-hole.  I feel like the latter case is somewhat unlikely.  In fact, the Mythbusters tried this in their first season and ruled it "busted".  Not exactly 100% scientific proof, but worth a note at least.

@DarrelHoffman Yeah, you definitely can't be sucked out through a bullet hole (unless we define 'bullet' to include large artillery shells.) You could literally just cover it with something to fix the problem. It's likely that the bullet hole is smaller than the outflow valve anyway and the cabin pressure could be maintained by simply lowering the flow through the outflow valve even if you didn't close the hole.

@alephzero, adding to Marks comment: 1. The mass of the person plays a role against being moved. 2. It's not sufficient to move the body, some speed needs to be achieved to actually prevent him/her to just oppose the move created by the the pressure differential quickly decreasing. 3. It's likely the airflow will create vortexes within the cabin and the problem is more complex. Last: For the windshield, the (dynamic) pressure is larger outside of the aircraft than inside, your explanation doesn't work.

Yes, it's real. Here's the official accident report on BA5390, which says:

The commander had been partially sucked out of his windscreen aperture

And:

The two men tried to pull the commander back within the aircraft [but]
  the effect of the slipstream frustrated their efforts

There's also Aloha 243 where one cabin crew member was ejected, although that was a really extreme case.

The amazing part of BA5390 is they were sure he was dead and were going to let him go but didn't want to because his body may have damaged the aircraft. Little did they know until after landing that he survived the entire ordeal.

@RonBeyer There's some nice British understatement in the report where it says the crew were "considerably reassured" when the pilot started kicking his legs :-)

It appears something similar happened on Daallo 159.

This also happened to a few people in some of the accidents where cargo doors blew out on the DC-10 and 747 a few decades back. Also, the idiot who tried to bomb an airliner in Somalia a few months ago was blown out of the aircraft.

Also I forget the name of the effect, but the air rushing past the hole at several hundred mph has a "suction" effect

@Pondlife: It's entirely factual. I posit that it's merely not a massive overstatement!

@JonStory The term you're looking for is the 'venturi effect'.

@JS. Thankyou! That's been driving me crazy for the last hour

@JS The Venturi effect refers to a reduction in pressure of a fluid passing through a constriction in a tube. The effect described is due to Bernoulli's principle. ICBW.

@AndrewMorton  You are correct.  Thank you for pointing that out.

@Pondlife I believe the copilot raised one eyebrow slightly.

At cruising altitude (say 35,000 feet), the difference in air pressure between the inside and outside of a comfortably pressurized aircraft is about 7 psi. If you imagine a hole just large enough for a person to squeeze through - perhaps 10 inches x 14 inches, that's 140 square inches; multiply that by 7 psi and you get 980 pounds of force - close to half a ton. If a hole that size suddenly opened up in an airplane, a lot of air would rush out very quickly and the pressure would quickly drop, but in the first few moments at least, there would surely be more than enough force to eject a person. For a small aircraft, a person would probably have to be right at the location that opened up to be "sucked out"; the pressure would fall off very rapidly with only a small volume available. For a large airliner like a 747, it could take some time for a significant amount of the air in the cabin to escape through such a hole, and there would be some pretty violent air movement near it, so an unsecured person could be ejected even from some distance away.
Two incidents (BA 5390 and Aloha 243) attest to the phenomenon, although the Aloha case was a more complex sequence of events. The investigation produced a theory that a cabin window blew out; the resulting depressurization effects caused a flight attendant to be blown into the aperture, momentarily obstructing the airflow; this produced a "fluid hammer" effect - an overpressure in excess of the structural limits of a corrosion-weakened airframe. This resulted in the "unzippering" of a large section of the upper fuselage. Despite the end result of the Aloha incident, it involved a person being effectively "sucked out" of a sudden opening in the cabin.

good info and rate calculator at tlv.com


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How do hot air balloons get started (without burning the fabric)?
I have seen photos of hot air balloons aloft with fearsome looking burners shooting flames into the interior of the balloon. That may be fine for a fully inflated balloon. But what about when the balloon is in a heap on the ground? How do you get it inflated without burning the fabric?

@abelenky We've been over that point multiple times in meta and chat (e.g. here, here). So far the general consensus is that we're here to answer questions, not to just send people to Google or Wikipedia. That also seems to be the general idea on SE as a whole.

The nice thing about trivial answers is they are easy to answer and expand upon, which makes them good for building rep and drawing people to the site.

@abelenky: It seems to me that the question is valid. Whether it's easy to find an answer elsewhere is not the point, nor the fact that the question will get many reputation points. While the question shouldn't be closed, if you find it not so good, then you are free to not upvote it, and if you think the OP makes no effort to find an answer prior to ask, then you may even downvote it. And by the way I believe your last argumentum ad personam on the chat is not something that is in the spirit of the site.

It's fun to hang around hot air balloon launching sites, sooner or later you'll see one on fire or at least getting totally melted by the blow torch (propane burner). I have!

The balloon is spread out on the ground and rigged to the basket.
Then, a cold air blower is used to do the initial inflation, blowing air into the envelope through the bottom aperture. This gets the balloon about 75% inflated, but still horizontal.
Lastly, the burners are lit to heat the cold air already inside the canopy, expanding it and raising the balloon to vertical and full inflation.
You can find any number of videos on YouTube that show the process. Here's one:

How important are the rabbit ears to the process?

Essential


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Should you sump fuel tanks when the fuel system is below freezing?
I recently saw an argument in a forum I frequent that sumping the tanks when the system was below freezing was a bad idea, as you can't drain solid ice from the fuel system, and there is a chance that ice may jam the drain open, causing your entire tank of avgas to empty onto the ramp.
While this is certainly a possibility, is it a reason to skip sumping the fuel system during preflight, or do the reasons for checking the fuel system outweigh the risk of a tank of fuel winding up on the ground?

I certainly know which side of this argument I wound up on, but I'm going to sit quietly on my hands for at least a day...

does Ice float or sink in fuel?

nvm, fuel is ~0.8 kg/l while ice is ~0.91 kg/l so ice sinks

Very good question.  I'm guessing the water would not freeze instantly as you drain it. Assuming it's not already frozen in the tank and that it's not 100 below freezing.  I would rather have a problem on the ground with my fuel draining on the ramp then my engine sputtering out while I'm in the air!

@zingle-dingle Water will happily freeze in a fuel tank - the "thermal interia" provided by the avgas means it won't freeze the instant it drops below freezing, but if it stays cold enough long enough you'll get ice (and conversely the same thermal inertia means it will stay frozen for a while after the temperature rises above freezing)

OK, I sat on my hands for a while, so now I'll stick my head in the lion's mouth.
You should absolutely sump your tanks every time you go flying as part of a routine preflight inspection, whether you've taken on fuel or not, whether the aircraft has been hangared or out on the ramp, and even if it's below freezing.
Water isn't the only thing you're looking for (misfueling happens - also bits of fuel tank sealant, rubber from a rotting bladder, dirt that made it past the fueling truck's filters, etc. - you want to find these things!)
Ideally if it's below freezing you should also pre-heat your aircraft so the engine, instruments, and fuel are above freezing when you're preflighting (which is generally accomplished by sticking the plane in a heated hangar), but sometimes that's not an option and you make do.

Why should you sump the tanks if it's below freezing?
Well like I said above, water isn't the only thing we're looking for - and all those concerns still hold valid no matter what the temperature is. Water is the one that people seem to come up with as a reason for not sumping when it's below freezing though, so let's talk about water:
There are five general ways water can manifest itself in your (Avgas) fuel system:

Liquid Water
If it's not been below freezing (or it's really sunny and your fuel tanks have acted like an oven) water may be liquid, waiting for you at the sump drain just like on a warm summer day. You'll drain it out and go on about your business.
Slush (ice crystals suspended in the fuel)
If it's below freezing you may have suspended ice crystals or slush in the fuel (particularly if you just took on fuel). This will look "cloudy" when you drain it from the sump and it's a good indication that today is not a good day to fly: you may have a LOT of water in the fuel, and you need to need to deal with it (warm the plane up and drain off the water, and figure out how so much of it got in there in the first place).
(There is a chance that slush could jam your fuel drain open, in which case your fuel tank will empty itself onto the ramp with great rapidity.)
Little bits of ice
Little drops of water can freeze into little bits of ice, which are often just too big to come out of the fuel sump drain, but just small enough to lodge in it and keep it from closing (which, again, will cause your tank to empty itself onto the ramp with great rapidity. This is also an indication that today is not a good day to fly).
BIG bits of ice over the sump drain
Liquid water will flow to the lowest point in the fuel system (the drains). If it's below freezing it will freeze there, potentially blocking the sump drain.
You'll notice this condition because the sump valve may feel stiff, your tank may not drain, or it will drain very slowly, possibly with water in the fuel.
This is a good indication that you shouldn't fly until you figure out what the cause of the problem is (it could be ice, it could be a defective valve, or it could be a bunch of other things, but until you know you want to stay on the ground).
Hidden Ice (big bits of ice away from the sump drain)
This is perhaps the most insidious: Ice that's not near the sump, and doesn't block or jam anything.  Hopefully you'll spot this sitting at the bottom of your tank when you look in to check the fuel level (you do visually check your fuel level, right?), but you probably won't notice anything out of the ordinary when you sump the tank.

(There are of course other ways water can hide out in the system besides the fuel tanks, but these are where you're most likely to find it.)
The most likely "bad thing" to happen to you in any of those scenarios is that your fuel sump will be jammed open by ice. This means you'll spill a tank's worth of avgas on the ground, and you'll have to call your airport's spill cleanup/emergency number and let them know.
That emergency is on the ground, and it may be a little embarrassing to have to explain to the spill cleanup folks, but it's better than the other possibilities.
The Bad Things that can happen to you in the air if you go flying with undetected ice/water in the fuel are far worse: The ice could melt and your engine could start trying to burn water, which doesn't ignite very well.
Check out Gene Benson's "Why Did They Do That? - Volume 2" presentation, starting at slide #7 for one example of how things can go catastrophically wrong if you neglect to sump your tanks (or ignore the warning signs when you do).

From your previous comment, you made it sound like you experienced (comically) one of these outcomes. Did I misinterpret?

@HCBPshenanigans I've never had an ice or water related engine stoppage, but I have found the occasional little bit of water in the tank after a heavy rain (never more than a pea-sized drop in the fuel though). I have had a fuel valve refuse to close on me once, but that wasn't ice: the little O-ring that seals the drain rolled up on me. I was able to get it to close by wiggling the valve (followed by having the drain replaced so it wouldn't do it again).

Unfortunately, the link "Check out Gene Benson's "Why Did They Do That? - Volume 2" presentation, starting at slide #7" appears to be broken now


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What should I look for / check during an oil change?
Piston aircraft engines require regular oil changes, and at least in the US it's something the FARs allow an owner with a private pilot certificate to do.
What are some of the things I should look for during an oil change (or what are some of the things I should be sure my shop is checking when they do an oil change)?

First, a word of caution - Don't attempt your own oil changes on an aircraft unless you're familiar with the process, and have both the tools and skills you'll need to get it done right.
  It's probably a good idea to have your mechanic supervise you on your first oil change, and check your work on the next few until you're sure you've got the hang of  it.
This isn't an oil-change how-to - just a list of stuff to look at to judge the general health of an engine.

Disclaimers and warnings out of the way, here's what I look for (or ask the shop to check) during an oil change:
Draining that dirty old oil
First, don't forget to grab a sample for oil analysis while you're draining (I'll talk about that a little later!).
Now, while the oil is running out of the drain you're really looking for big chunks of metal coming out with it (or heaven forbid blocking the drain hole) You also want to make sure there is no nasty sludge coming out (that's a car in the video, but the principle is the much same).
Basically what's coming out of the drain should look like oil. It'll be dirty (dark to black, rather than the pretty clear-ish liquid you poured into the engine all those hours ago), but it should still be flowing nicely.

Obviously chunks of metal here would be bad. If you're noticing them in the drained oil you've got some serious mechanical damage in your engine and you need a mechanic to check it out.
Sludge generally means you need to talk to your mechanic too - often it means a bunch of low-time oil changes to clean out the gunk from the engine, but if it's severe it could indicate other engine problems that need attention

Checking the Oil Screen
If your engine has an oil suction screen that can be removed and cleaned (as on most Lycoming engines), remove it and inspect it for any pieces of metal, then clean it and reinstall it.

As with chunks in the drained oil, bits of metal in the screen are often a sign of a serious mechanical problem - if you find any you're going to want to talk to your mechanic.

Inspecting the Oil Filter
As part of every oil change the filter should be cut open and inspected for fine metallic particles in the pleats. There are a few of ways to do this (one is to simply stretch the pleats out under a bright light and look at them, another is to wash the filter in a solvent and strain the used solvent through a coffee filter to see if any particles are left behind).
EAA has a great video on inspecting an oil filter - it's worth the 10 minutes to watch.

If you find any bits of metal  in the filter you already know what I'm going to say -- you're going to want a mechanic to check things out. A very small amount of metal may not be a serious issue, or it might be the beginnings of an engine on a path to self-destruction.

Run an oil analysis
Some people do an oil analysis every oil change, some people don't ever do one.
Smarter people than me say it's probably a good idea to do them, so I consider it to be cheap insurance and a good window into where those "bits of metal" I keep talking about above might eventually start coming from.
There are plenty of companies that do aviation oil analysis and for an idea on what's in the report check out Blackstone Labs' interactive report explanation page.
There's another EAA video that talks about oil analysis which is worth the 3 minutes to watch too...

Note that a single oil analysis won't tell you much (unless things are REALLY out of whack) - it's the long term stability or trends that matter here, so if you're going to do an oil analysis be prepared to do them at every oil change from now on...

Do the things that aren't oil-related
An oil change is a good opportunity to do some other regular maintenance - Since the cowling is off anyway why not clean/gap/rotate your spark plugs (which is another mind-numbing task the FARs allow owners with a private pilot certificate to do)?
In fact since the cowling is apart and your engine is naked now's the time to give it a good once over for any loose parts, chafing wires, etc. that might have come up since the last oil change or service that had someone under the cowling.
It's probably also a good opportunity to check all your lights (interior and exterior), and break out the manufacturer's lubrication chart to see if there are any other things that need to be oiled, greased, cleaned, or sprayed.

So what's all this fuss about metal?
You've probably noticed above that I'm really harping on all the ways you can find metal in your oil in this answer.  The simple fact is that all engines wear, and eventually they wear out. That wear shows up as microscopic bits of metal relatively harmlessly suspended in the oil (what the oil analysis picks up), but if that wear suddenly accelerates bigger pieces of metal start getting torn off of the moving parts in your engine, and showing up in other places like the oil filter and screen, letting you know something is wrong with your engine, and hopefully letting you know on the ground rather than in the air.
I don't want to give the wrong impression here though: Not every bit of metal that turns up in an oil filter will be a death sentence for the engine that produced it! In fact brand new engines sometimes produce a few bits of metal during break-in as parts wear in to each other, and they stop after the first oil change or two. The thing to remember is any metal showing up where it shouldn't be during an oil change is definitely something to have checked out by a mechanic.

Nice question and answer. I like to add, that there are strainers available you could use during the oil change. This is still a safe way to check the oil for metal parts without cuting the filter. Anyway the filter check is still the safer way and should still be done if you find something in the strainer.

Another note is to clean the drain area thoroughly before starting the draining so that when you take your sample, it won't be contaminated with dirt or whatever. Also, if you use a drain hose, make sure it's clean for the same reason.

@Falk The strainers are definitely a good tool to use while draining, but I'm not sure I'd use them in lieu of a filter cut (What if the filter has been doing a really great job and no little whiskers made it back into the sump? -- Not too likely, but possible.)

Definitely. I've learned to do this basic maintenance on aircraft which are used very often and where oil was changed every 50 hours, so we had some very good idea of the condition and simply preferred to avoud this check - it was definitely a reduction in safety but wecstill checked the filters every 100 hours. If someone's doing this checks on some not as often used aircraft you shoul avoid being to lazy, it effects safety. Maybe consider the age of the engine the hours since the last oil change, the type of operation and temperatures before making a decision.


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How/Where can I get additional weather information for flight planning?
METARs, TAFs, the area forecast (FA), and flight service briefings are great tools, but if I'm planning a flight with an overnight stay (or a flight that itself might take me a couple of days of travel time) I often feel that the weather picture I'm getting is a little too short-term for my liking.
Aside from watching The Weather Channel are there any supplementary weather sources I can look at which are useful for aviation/flight-planning purposes?
I'm interested mainly in resources for the USA but answers for other countries would be interesting too.

Honestly, for long term I usually just use the weather channel's website.  There are also the typical long term aviation graphical forecasts that show long-term forecasts, but they don't show temperatures (which are sometimes important).

I use the weather channel for anything more than 3 days out myself, but I find it to be "sketchy" - Generally if I don't know what's going to happen weather-wise their reports seem to be equally uncertain. (Why do we pay these people money again?)

The Meteorological Service of Canada (MSC), the United States National Weather Service (NWS) and the National Meteorological Service of Mexico (NMSM) have a joint project called North American Ensemble Forecast System (NAEFS). I've referred to it in the past to get some outlook on temperature and precipitation amounts more than a couple days in the future.
From the NAEFS site:

NAEFS combines state of the art ensemble forecasts, developed at the MSC and the NWS. When combined, the grand ensemble can provide weather forecast guidance for the 1-14 day period that is of higher quality than the currently available operational guidance based on either set of ensembles alone. It allows the generation of a set of forecast products that are seamless across the national boundaries between Canada, the United States and Mexico.

In Europe, several national meteorological services provide additional info (sometimes on a paid basis). Some other services cater e.g. especially to glider pilots. Examples:

http://www.flugwetter.de/ ($)
DWD - Deutscher Wetterdienst Luftfahrt  (free)
http://www.meteoschweiz.admin.ch/web/de/services/aviatik.html ($)
http://www.nzz.ch/wetter/thermikprognose/ (free)
http://wetter-jetzt.de/  ($)
...

There are also a number of private websites run by clubs and/or enthusiast pilots, e.g. http://www.schaenissoaring.ch/wetter_berichte.cfm?SelectedMenuID=154 or http://www.alpenstreckenflug.de/wettera.htm which offer excellent (curated) information, sometimes on very special conditions like mountain waves etc..

Please feel free to edit in any source you prefer...

In my eyes, it's always a good idea to call WX BRIEF the evening before your planned flight (if you don't know your registration at this time, the pilot's last name is sufficient) and ask for a outlook briefing. Before you call check the TAFs and SIGWX charts available at http://aviationweather.gov/products/swl/ so you have a good idea what the briefer is talking about. These guys are really helpful and especially when you call in the evening hours they take a lot of time to discuss the weather situation with you and even answer related questions or suggest other weather sources which may be helpful for your particular operation.
For you who don't know WX BRIEF: it's a free number 1800WXBRIEF (18009927433) you can dial in the US to get a standard, abbreviated, or outlook briefing. This service is provided by Lockheed Martin flight services.
If you need help to interpret weather information you will find the answer to your question in Advisory circular 00-45G.

A telephone briefing is certainly an important part of pre-flight prep (not just for weather - I've had flight service briefers give me airspace information that wasn't in my DUAT briefing). That said, I've found their weather skills to be hit or miss - some briefers are excellent (and have sufficient weather knowledge to actually offer some insight), and others... not so much. (I find it helps if you specify your state when requesting the briefing so you don't get someone halfway across the country who doesn't know your local area's weather patterns.)

Yea, that helps absolutely. I'm not long in the US but I've already made this experience. I can't really evaluate their weather skills yet, but anyway, as I've already mentioned,  I'm a fan of getting your own sight of ghe weather prior calling wx brief and then using the possibility to get a second opinion on it or even have someone to discuss the weather,  what's obviously possible only if the guy on the other end of the line knows what hes talking about.

Oh and, by the way, thank you for editing the link ;)

One tool I use which is not aviation-specific is the NWS/NOAA Area Forecast Discussion.
This is a text-based collection of notes from the forecasters at regional National Weather Service offices, and I've found them to be full of useful "tribal knowledge" about weather patterns in an area.
I've found the most useful sections are the synopsis through the long-term (about 1-week) discussions. There is a brief aviation-specific section as well, which is also available on aviationweather.gov

I have all of my students read this every day along with their weather briefing. Knowing not only what the forecast is but the confidence level of the people making it is invaluable.

The (experimental) High Resolution Rapid Refresh model is pretty awesome. It's got a huge selection of plots and some aviation-specific filters. It's not particularly forward looking, though.
Most non-aviation forecasts are going to be pretty low detail, unfortunately. I would tend to stick with NOAA source data rather than third party stuff, as I doubt most websites are actually using custom climate models. The NOAA Climate Prediction Center has an 8-14 day outlook composite that might be somewhat useful.
A good NOAA source you didn't mention is http://aviationweather.gov, which has a more classic aviation focus in its available data. It has longer-term forecasts, but they often are graphical, low-resolution, and not of particularly great use for long term planning.

Do either of those have long term forecasts (more than the standard aviation forecasts)?

HRRR is higher detail over similar periods, so, no, I suppose not. He hadn't specifically mentioned aviationweather.gov so I wanted to get it here as a resource. It's got some longer scope charts but they quite frankly are pretty bad.

HRRR is actually news to me - it seems like a tool with a lot of potential.

HRRR is awesome. It's just not really the right tool for your question. :)

It's paid content but the weather briefs from http://avwxworkshops.com/ are great.  I have used them to help take my light plane across the country twice.  Considering the importance of weather, I think membership is a good deal relative to the other costs of flying.  I'm not affiliated, just a happy customer.

As you mention that you are interested for resource in other country other than USA, here is the TAF, METAR/SPECI for Hong Kong International Airport(VHHH/HKG), ang SIGMET for HKFIR(VHHK). You may access them though http://www.hko.gov.hk/aviat/amt_e/wxobsfc_e.htm


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Why do airliners hug the coast on flights?
In reviewing the route a commercial aircraft is taking from Boston to Miami, I see the following:

As you can see, it does not follow the great circle path and in fact deviates significantly from it, being about 10% longer. The aircraft is happy flying over water over the coast of New Jersey and New York, but then later becomes water averse and hugs the coast off of South Carolina, Georgia and Florida.
In North Carolina, the aircraft even veers completely off course briefly, heading about 255 which is nowhere near the direction it needs to be going to get to Miami.
What is the explanation for this, if any? It looks kind of random, almost as though were no logic beind it.

First you say "hug the coast" and then "It looks kind of random, almost as though were no logic beind[sic] it."  Desire to hug the coast is the logic.

The reason is that the aircraft has filed a route along airways and not a direct (great circle) route. In most countries, an IFR flight cannot just file a direct route and they have to use airways. An exception would be countries with Free Route Airspace.
The flight you show looks like AA747 from 26 Jun 2021 on FlightAware. If you follow that link, it will show you the route they filed on the right:

SSOXS5 SSOXS BUZRD SEY HTO RIFLE J174 ORF J121 CHS CAKET Q97 JEVED Q97 KENLL OMN HILEY7

Here, SSOXS5 is the SID and HILEY7 is the STAR. Everything in between is the filed route. You can type the same route into SkyVector to view it on a map of high altitude airways:

There are no airways that would be a direct (great circle) route from Boston to Miami, so the reason they don't go over the water during the first half of the route is simply that there are no suitable airways.
During the second half of the route, the situation is a bit different. There are some airways over water that would provide a more direct route. If you look at the route they flew the next day on FlightAware, then you can see that they used these airways:

You can also see that the flight on 26 Jun deviated from the planed route (the kink in South Carolina). The reason for not using the shorter airways and for this kink is likely the presence of thunderstorms along the route. You can see them on your FlightAware screenshot as the yellow and red patches. The flight crew probably asked for a different route for weather avoidance. Here is a zoom of the region, where they deviated from the route:

You can clearly see the single thunderstorm cell directly in front of the original route.

@TobySpeight Thanks for your suggested edit, but the quote is from this FlightAware page, which does not contain such arrows. SkyVector automatically produces them when pasting the route.

I suppose a follow-up question would be "How much time/fuel/money would've been saved by going on a more direct route?"  (Assuming there aren't storms in the way of course.)  I'm guessing not enough to make a significant difference in this case.

@DarrelHoffman It can certainly make a significant difference. The question claims a 10% difference between this route and the great circle route (although that includes maneuvering after takeoff and for landing). Even 1% fuel saving is significant for airlines. The problem is that airways exist for a reason: to manage traffic flow. The US east coast is obviously very busy. But other regions in the world have already implemented Free Route Airspace. My guess is the US will follow eventually, but it takes time to implement the required changes to the traffic flow procedures.

Since North America is a large landmass, low-cost airlines operating domestic flights can save money by not providing the additional safety equipment (and flight crew / cabin staff) required for operations over water. No point in flying a plane full of life jackets, and spending time every flight on passenger safety briefings on how to use them, if you never are going to use them,

@alephzero Are you sure about that? I don't think I've ever seen a commercial aircraft without life vests, at least not in the US. After all, water landings are always a possibility even when you aren't flying over oceans. Many airports have runways immediately adjacent to bodies of water (SFO and LGA come to mind). And who could forget the Miracle of the Hudson, a domestic flight from LGA to Charlotte? There are also the great lakes to consider.

@KevinKeane There are different rules depending on the types of water bodies overflown and for how long, and different levels of equipment are required. See https://aviation.stackexchange.com/questions/67348/what-and-where-are-flotation-seat-cushions (which actually specifically mentions US Airways 1549 and the possible lack of life vests due to not being EOW).

@alephzero And periodically checking them, and replacing them...

What a thorough, fantastic answer to a great question!

It's entirely possible that the flight in question was originally intended to use the route taken by the next day's flight, however, the pilots looked at the incoming weather and decided to fly behind it for avoidance, instead of flying ahead of it and having nowhere to go but through it once the two expected courses intersected.

Aircraft are also limited how far they can get from the coastline based on the survival equipment aboard the aircraft. Not every variant of the same aircraft has the same equipment.  Some aircraft are limited to 50 nautical  miles while some can go up to 400 NM. It's not just life vest but also life rafts.  If you want to know more, research the CFRs on limited over water and extended over water aircraft.  Carrying extra equipment is weight. Weight cost money to haul around.  So it doesn't make sense for every aircraft to be certified for extended over water operations.

See https://aviation.stackexchange.com/a/67386/3313 for details

Except we see that they did fly over a much longer stretch of water doing the same flight on the following day - Though it's possible it wasn't the same plane both times?  If it was, I don't think they were loading different water survival gear on it from one day to the next...

Aircraft are used on multiple legs everyday and not necessarily on the same route.  So the chances of that same aircraft used on the next day are low.  Also, aircraft air dispatched by planners based on routing.  If say another route is needed for weather, that requires over water an aircraft  change would be required.  Equipment is not swapped also between aircraft, as the interior placement where the equipment is kept varies even between same aircraft types.  Thus is all certified by the FAA.


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What dictates the shape of the attitude indicator display on the PFD?
I notice the atitude indicator displayed in the PFD is either squared-shape or truncated-circle-shaped.
A good example of the square shape is the B747-400, It looks like a square whose corner are a bit rounded:

(Source: airliners.net)
A good example of the circle-shaped is the SAAB2000 or the A340:

(Sources: airliners.net and airliners.net)
They look like a circle whose both right and left sides are truncated to display rules (speed and altitude).
In either case, the information displayed are the same (pitch, bank angle, perhaps flight director,...) and are displayed in a very similar manner (including the colors). Those 2 designs exists for years, so there may not be advantages of one over the other.  Why one is preferred over the other for some manufacturer, and the other one for other manufacturer? What criteria are taken into account when choosing this shape?

One could imagine the 747's indicator as a larger round display with both the vertical truncation for the speed/altitude tapes, and horizontal truncation because that's all that would fit on the screen. (Though the screen in this case is tall enough for a rounded top.)

On many aircraft, the same model can have both according to customer choice!  A single PFD computer can generate multiple different displays.  It an even be changed after delivery if the customer wants a different display.  Why choose one?  Commonality with other models in the fleet?  Graduation path for FOs to reduce difference training?  Customer preference?  Legacy?  In other words, you can find two 744s with different  operators with the same hardware but different displays.

Links are dead now, thus question becomes worthless for future readers. Could you provide updated ones ? Can't find them on airliners.

Just adding that the latest fashion is to use full screen for attitude indicating (sometimes even with terrain model) and overlay the rest of the primary information on top (search for 787 PFD or Garmin EFIS / Garmin Synthetic Vision).

Notice that the circular one follows the inside of the bank angle arc, which means the bank ticks have a higher contrast (against black vs sky) and thus easier to read.

A circle makes sense because a physical attitude indicator is round. (A physical one has to be round because it consists of a ball moving behind a window.) It makes the screen display look more like the instrument it replaces, which is good for recognition and familiarity, and makes it easier to judge things like bank angles.
A rectangle makes sense because it has to fit on a rectangular screen. You can tile rectangular instruments/displays on a screen efficiently, with no wasted space between them, as your example shows with the tapes. Rounding the corners delineates the edges of the display better than just having abutting rectangles.
The full process by which physical cockpit instruments and glass-cockpit displays are designed and laid out is too long to explain here. The main focus is on making it hard to make mistakes, and after that to make it quick to see the most important information. To support this, each instrument has to be easy to identify and to read correctly. Despite the shape difference, the two designs look very similar. Even if you've never flown any of these aircraft before, you'd immediately recognise it as an attitude indicator, and you wouldn't confuse it with a different instrument.


text:
What is automatic control connections and how does it work?
The Rolladen-Schneider LS4B control connections are automatic. This feature, also called automatic control hookup seems to be common. The last time I assemble a glider was more than a decade ago, and controls had to be mechanically (re)connected one by one.
What is automatic control connection? (I imagine it is some mechanism connecting controls when assembling wings). How does it work?

The automatic hookup uses a catchment area to mechanically force the pushrod into a receptacle to ensure a proper mechanical connection when the parts of the plane are connected.
As an example, I have sketched below how the ailerons would be connected. The blue structure is the fuselage-side part, and the green structure is the wing-side part of the control linkage. The pushrod coming from the stick is connected to a trapezoidal cone which is hinged at the same point as the wing-mounted pivot lever which is moving the pushrod connected to the aileron.

The opening of the trapezoidal cone is sized such that the end of the pivot lever will always be caught by it, regardless of the stick position and the aileron deflection. At the base where the end of the pivot lever rests when both parts are connected, the exact position and play between both can be adjusted, so the automatic connection will not have an adverse effect on handling.
I once witnessed an aborted winch launch of the SB-8 in which the linkages to the ailerons were interchanged. The pilot noticed the wrong operation of his ailerons before becoming airborne and released the rope quickly, but could not avoid a ground-loop, because he had pushed the low wing into the ground when trying to correct the plane's attitude. I was glad not to have been in his position, because I am not sure I had reacted as quickly. Automatic connections would have made this mishap impossible.

Automatic control hookup means that when the wing or tail are fully inserted into the aircraft fuselage, that the control rods for the airlerons, flaps, speedbrakes, elevator, etc., are all guaranteed to be fully and properly connected to the control handles inside the cockpit.
Without automatic control hookups, the control rods coming from the wing or tail control surfaces had to be manually connected, one by one, to the control rods coming from the cockpit. This system led to many accidents, when pilots forgot to connect a control rod during assembly, and they didn't find out until the glider was launched:

Source: http://www.blackmountainsgliding.co.uk/cfidocs/accidentreviewbga12.pdf
Another type of manual control rode failure is associated with the L'Hotellier connector, which would seem to be fully connected, but would fall apart, even after a positive control check.
Automatic control hookups are designed to reduce, if not eliminate, these kinds of problems. Needless to say, even with automatic control hookups, a positive control check must still be performed before every flight.

This system led to many accidents, when pilots forgot to connect a control rod during assembly, and they didn't find out until the glider was launched because they failed to perform a proper preflight inspection. <--  Fixed that for you :)


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Are helicopter with coaxial rotors equiped with blade flapping mechanism?
Helicopters with coaxial rotors such as the Ka-27 don't need mechanisms to overcome dissymmetry of lift as there is advancing blades on both sides of the helicopter. A common mechanism to overcome the dissymetry of lift on classic helicopters is the blade flapping as described here.
I see no need to introduce blade flapping on coaxial rotors helicopters, but there can be other reason to keep it I don't know.
Are helicopters with coaxial rotors such as the Ka-27 fitted with blade flapping mechanism?

Yes and no, but mostly yes, especially the Kamov family.
Here's a picture(Wikipedia, CC-SA) that shows the (pair of very complex) flapping mechanism on Ka-27. Even though two rotors together should be able to balance out the asymmetric lift, the rotor hub and rotor for each individual rotor isn't rigid or strong enough for handle its own asymmetry (when it happens accidentally, e.g. the receding blade stalled, the receding blade of the top rotor will bend down and hit the advancing edge of the bottom rotor bending up and cause a catastrophic failure, e.g. Ka-50 had a series of rotor collision accidents).

However, there are rigid rotor helicopters and these don't bend nearly as much and don't need to flap, but none of them are among the Kamov lineage.
This is especially useful for high speed helicopters (e.g. Sikorsky S-97 Raider) because no amount of flapping will generate enough lift before stalling to cancel out the lift asymmetry, for the receding edge is too slow, so it has to let each rotor remain asymmetric and let the two rotors cancel each other.


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Do airlines staff extra crew members when disabled persons are check in?
The question "How are disabled passengers evacuated during emergency?" made me wander if minimum crew number required by regulation are enough in case of passengers requiring extra care in case of evacuation.
My question is restricted to cases where airliners know in advance that a passenger with reduced mobility, unable to run or jump (let's say the passenger requires either a wheel chair or crutch to walk) is scheduled on a specific leg. Do airlines staff extra cabin crew member(s) to improve handling of everyone in case of emergency evacuation?

In almost two decades of flying for airlines, I've never seen it done, and never heard of any program to facilitate such staffing.


text:
What is the heaviest aircraft fitted with a central control stick?
Primary control surfaces for roll and pitch are controlled either by a wheel (C-172, Concorde, ...) or by a center-stick (mirage 2000, most gliders, ...). Wheel tend to be used for bigger aircraft. E.g. I don't know any airliner fitted with a center stick.
What is the biggest aircraft (highest MTOW) fitted with a center-stick? (Airbus style side-stick are excluded.)

You have for some reason omitted sidesticks from the (original) first paragraph of you question. They are a very common control interface, therefore you cannot just say ...roll and pitch are controlled either by a wheel or by a center stick.

@ymb1 i was first thinking of joystick, but given my initial wording and the fact that an answer already exists I think the location matters more (i.e. space shuttle's input are not excluded)

The biggest I can find is at 585,000 lb the C-17 has a center stick but depending on what you mean by "airbus style" this may be disqualified.
Other contenders:

The SR-71 had a MTOW of 172,000 lb and had a center stick
If you consider the time it spent in the atmosphere as qualifications for "aircraft" at 240,000 lb the Space Shuttle had a center stick

By biggest, I mean highest MTOW. For the space shuttle such value is irrelevant as she doesn't take off from a runway.

@ManuH i have updated to reflect, i left the shuttle MTOW since it is an officially listed value but your point is noted.


text:
How does a delta wing deal with supersonic boundary separation?
The question Why most of the supersonic or fighter aircraft use all-moving control surfaces? emphasis the importance of all moving stabilator for supersonic aircraft.
Many supersonic aircrafts fitted with delta wings (Concorde, mirage III, mirage IV, saab draken, sr-71,...) rely on elevons only for pitch control and thus cannot use a all moving stabilator.
How do they overcome the reduced controllability due to the boundary separation of the airflow at the trailing edge of the wing?
My question is focused on aerodynamic solutions (I know some aircraft can shift there CG thanks to trim tank, and some fighter are not aerodynamically stable in pitch but I want to focus on the boundary separation issue).


text:
How much does a passenger-to-freighter conversion cost?
Transforming a passenger airliner to a freighter seems to be common. If I understand correctly (do not hesitate to correct me), it basically consists of removing many components (seats, galley, ...) as done in the first phases of a D-check, and then the handling equipment is added (as it should be done in the late phases of a D-check for freighters).
How much does the transformation cost compared to a D-check?
Related: How much does a D-check cost compared to a new aircraft? (Useful to have an idea of D-check costs.)

#TIL: manutention. I did not know that was a word.

Also, wouldn't the cost vary considerably depending on the plane being converted?

@FreeMan Yes, as D check. I expect both to vary the same way.

@FreeMan manutention is a french word. I thought it was the same in english (my bad, edited)

There is considerably more to P2F (passenger-to-freight) conversion than just stripping stuff out and inserting handling equipment. In this photo of a newly-converted A330, the green primer shows where the fuselage has been reinforced; notably, an entirely new framework to take the cargo door, but also the existing frames all the way along the fuselage.

No worries, @ManuH! there was a definition for it as an English word as well. Plus, I learned a new word!

@Fiddlesticks -- why is primer showing on the outside where frames have been added?  To cover the rivet heads?  Could be the basis for another question I guess.


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Why do we commonly use a "/" in acronyms in aviation world?
In non-aviation world, separation between letters in acronyms is either nothing (e.g. URL) or a point (e.g. A.M.). But in the aviation world, the "/" is common (e.g. G/S, V/S).
I'm puzzled as:

some acronyms never use "/" (e.g. ATC)
some acronyms almost always use the "/" (e.g. V/S")
some abbreviation use this separator but are not acronyms (e.g. A/THR, THR containing more than one letter)

Why is this separator so spread in this worlds ?
Why some acronyms does not use this separator ?

I think it is not only common in the world of aviation but in the English language in general. Think of "a/c" for aircraft and "a/c" for air conditioning. But indeed, I find this funny as well.

@PerlDuck I'm not a native english speaker, that may be why I find that weird :) . Yet, I'm still puzzled (as explained in the question).

I think it’s useful as a separator in abbreviations (e.g. for A/THR you immediately see which group of letters stand for which original word) so it helps as a visual indication of what it is you’re reading. The dot would double as a separator of sentences and inside abbreviations, and since uniqueness of symbology is always a good idea, the slash helps there, too. Can’t say that’s the reason, but at least that’s why I like it.


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On an A320, will the aircraft compensate for constant pilot rudder input?
As I understand from answers to the question What does rudder input control in normal law in an A320?:

the rudder deflection is the result of the sum of pedals input and plane's FBW command
in normal law, the FBW tries to fly with zero slip angle

This seems reasonable so that any asymmetry is automatically compensate.
But what happen if this asymmetry is due to constant non neutral pedals'input?

The rudder of A320 is fully mechanical. So, the control laws do not govern its movements. In normal operations, the rudder is controlled by FAC (Flight augmentation computer) and it gives three main functions. They are:

Yaw damping and turn coordination.
Rudder travel limiting through the rudder travel limiter (controls the rudder deflection angle based on speed).
Rudder trim.

These three functions are not fly by wire related. As a matter of fact, most modern conventional airplanes can perform all of these functions. Even the Dash 8 classics I flew a few years back, had yaw damping, turn coordination and rudder travel limiting.
When in flight even with auto pilot on, the rudder can be overpowered by the pilot and the computers would not intervene. And if you apply enough of a force, the auto pilot will disengage. In the event of FAC failure, the aircraft rudder can still be operated as long as you have hydraulic power. But the three rudder functions it provide will be lost. According to FCOM in a dual FAC failure, the rudder should be handled with care because the rudder travel limiter can no longer control the ruder deflection angle.

Now that the theory is cleared, I will try to answer your question. If a pilot applies constant rudder inputs in an A320, the aircraft will react to those inputs and the computers would not prevent the pilot from doing so. This is because there is a direct connection between cockpit pedals and the rudder and no computers in between. But constant fast rudder movements can lead to a very bad situation. Since the introduction of A300-600, Airbus started using variable stop rudder travel limiter systems. In a variable stop limiter, not only is the rudder deflection reduced with increasing speed, but also the pedal movement in the cockpit. This means, at very high speeds, very small deflections on the rudder pedals can generate heavy loads on the rudder and the vertical stabilizer itself. Basically, the rudder pedals become extremely sensitive at high speeds.
I am pretty sure you have heard about the American Airlines Flight 587 https://en.wikipedia.org/wiki/American_Airlines_Flight_587. According to the NTSB report, one of the reasons that caused the crash was the use of variable stop rudder travel limiters on Airbus aircraft. This was a factor that lead the pilot to unknowingly over control the aircraft (but there is no hard evidence for this). The FAA has been fighting with Airbus regarding this matter for years. But Airbus have not changed the system arguing that proper pilot training is what is required. But they brought a change and it was to give an ECAM alert if too much rudder input is detected. The ECAM comes with a warning light, an aural alert and a red "STOP RUDDER INPUT" message appears on the Primary flight display (PFD).


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What was in the noses of airliners before the weather radar?
At the time of the first Lockheed Constellations, airliners fitted with a weather radar were not common, and the navigator was not placed in the airplane nose. Thus, the nose seems to be mostly dead space.
Was the nose dead space with no useful equipment in it, or was it used for equipment I don't know about?

One data point here.  I have seen a DC3 with the nose opened up (hinged on top).  It had some electronics up there.  Not much, but it was basically an E&E bay.

Maybe a frog in a jar with a ladder?

Machine guns!!!

Older aircraft noses had a lot of hair.

@HotLicks I was thinking "bombardier"

Lights? Radio equipment? Plenty of other instrumentation to put there.


text:
What is the maximum holding time?
When arriving at a busy airport, airliners may be stacked in holding patterns, increasing flight time. I know airliners are required to carry extra fuel in case of rerouting (including a safety margin).
Once in holding pattern, aircraft may be reordered (not as simple as a FIFO), thus some aircraft may stay longer in their holding pattern.
Is there a legal maximum time an aircraft can stay in an holding pattern? If needed, the question may be narrowed to EASA and FAA regulations.

There is only so much gas in the tank...

At least in the US, there isn't any maximum holding time. The FAA's ATC Orders 4-6-1(c) give instructions for controllers, and they're allowed to issue an "indefinite" delay:

When additional holding is expected at any other fix in your
  facility’s area, state the fix and your best estimate of the
  additional delay.
[...]
When holding is necessary, the phrase “delay indefinite” should be
  used when an accurate estimate of the delay time and the reason for
  the delay cannot immediately be determined; i.e., disabled aircraft on
  the runway, terminal or center sector saturation, weather below
  landing minimums, etc.

The final decision on how long a hold lasts is really made by the pilot, not the controller. If a hold is taking so long that fuel is running low, the pilot can always choose to divert to another airport or declare an emergency for priority handling. This question might also be helpful.

No, there is no limit. Aircraft stay as long in holding patterns as they have fuel on board.

Actually that happened recently.  For operational/load reasons, JFK needed to use tailwind landing runways, making them too short for the weight of an A380.  The A380 asked controllers for a more suitable runway but they were unable to break the flow enough to allow that.
(I also wonder if this A380 pilot was conservative, and other A380s were landing while he orbited.  Perhaps his particular plane was heavy.)

The A380 clearly communicated their time available for holding before they needed to divert. As that time grew closer, controllers said "ain't gonna happen" and they diverted.
Anyway, there you see the mechanism: the pilots plan a divert, and from that, they look at fuel and decide how long they can hold. They tell ATC that if it's helpful.

There is no time limit. The aircraft may be holding until the pilot requests a diversion, or declares an emergency, which they will do depending on fuel on board.

I know airliners are required to carry extra fuel in case of rerouting (including a safety margin).

Actually not really. The required fuel is calculated as fuel needed to fly to destination, abort approach there and fly to alternate, certain time holding at alternate, and final fuel reserve.
The contingency fuel, for cases of route changes and holding is at pilot discretion. These rules mean that once the contingency fuel is burnt, the aircraft shall divert to  alternate unless it is clear they will be able to land soon.
The pilots are also supposed to declare fuel emergency when landing with the final fuel reserve still on board is no longer ensured with the distance left and any expected delay. And once that happens, the pilots can leave the hold at their discretion.
It should be noted that these days holding usually only occurs when there is some disruption like thunderstorms crossing the airport. In good conditions the flow control mostly takes care of releasing the aircraft for take-off so they arrive at approximately regular intervals and rate that the airport can handle.


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Is fuel in trim tank usable?
Some aircraft (A380, Concorde,...) are equipped with a trim tank in the tail. Transferring fuel from or to this tank help controlling the CG. This feature can only be achieved if there is fuel to transfer. If tanks are nearly empty, and CG must be kept aft, this fuel could not be usable, except if there is another mechanism to compensate for the CG.
Is the fuel from trim tank always usable? Does it count when calculating minimum fuel requirement for a travel?

Here's a good pilot write up of the A380's fuel systems:
https://captaindave.aero/2017/09/07/the-a380-fuel-system/
Of particular note is this paragraph:

Towards the end of the flight there are two additional fuel transfers. Any fuel remaining in the trim tank when the time remaining to destination drops below 80 minutes is pumped forward. Similarly, when the time remaining to destination drops below 30 minutes any fuel left in the outer tanks is moved.

So, clearly, on the A380 not only is the fuel usable but it's also a standard operational procedure to utilise it.
I would expect that any fuel trimming is either

Contingent on having more fuel outside of the trim trank. As that fuel depletes, the trim will change, necessitating (or at least allowing) the movement of fuel back away from the trim tank

or

The change in trim is about optimisation, rather than keeping the aircraft within safety tolerances. On a long trip in a large airliner, small changes in trim could have real impacts on efficiency and fuel usage without necessarily impacting control and safety.


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Is there a required check before selling an airliner?
In France, when selling a car, the last check (more or less a C-check) must has been done within the 6 months before the owner change.
Is there an equivalent requirement for airliners? I'm more interested in ICAO's rules.
I'm thinking of budget airlines that tend to sell their aircrafts while still young (less than 10 years) and thus having been subjected to at most one D-check.

I'm not aware of any such time limit or window requirement related to maintenance programs that apply to the legality of sale transfers, and couldn't find anything myself, so I'll proceed based on the assumption the answer is "no" but would be very pleased if someone who knows can correct the record.
Airliners or aircraft in general are not required to be sold "mechanically fit" like a, car, as a condition of sale, or fit with the last x months or years.  Regardless of who owns it or when it's transferred, it's airworthy and can be flown, or it's not, and can't (except for temporary permit to fly when you want to ferry an airplane from point A to point B, which you would do if you bought an un-airworthy but mechanically fit aircraft and wanted to get it to your own base).
So if an airliner is sold with a D coming up, there's nothing stopping the transfer from one owner to the other, even if it's at its D check interval limit and is grounded until the check is performed.  The new owner can purchase it and apply for a ferry permit, or a short term extension to the D interval (there is usually some latitude allowed for special situations).
If I was buying an airliner that was only a thousand cycles short of a D, well that is maybe 6 months or 8 months of flying or whatever, and I might specify that the seller complete a D check as a condition of sale (as well as incorporation of all outstanding Service Bulletins), or, I allow for the risks in taking it with the unknowns of a major structural inspection coming up with this risk factored into the price (this can be evaluated by analysing how the airplanes of that type are holding up at D check across the fleet - some airplanes already have pretty onerous structural patching requirements by then, imposed by surprise results during fatigue testing).

Most places I'm aware of (in the US) have no requirement of a car being mechanically fit for use prior to sale. If there were, BringATrailer couldn't exist! That's a bit of a side note, but I thought I'd mention it.

@FreeMan prepare to be shocked...  NY has an annual inspection requirement, like an aircraft, and it has to be current prior to sale  https://dmv.ny.gov/inspection/inspection-requirements.  Oddly enough, in Quebec to the north, probably the most "European" jurisdiction in NA, it's libertarian-ville.  No safety inspections, no emissions inspections, no inspection before sale, EXCEPT a one-time safety inspection when you bring a car in from out of province.  Ontario only requires an inspection to prior to sale, but they give 2 week temps if you want to do it after.

I did say "where I'm aware of"... So I can't buy a non-running car in NY state with the intent of fixing it up to use? Doesn't surprise me, but that's a topic for a totally different forum...

Yeah I know lol.  Pretty tough when you have 50 jurisdictions. Perusing that web page, if you buy a car on a private sale, they give you 10 days. I think the motivation is because the cars rot out and become death traps so fast due to salt use.


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Do glider pilots require normal headsets?
When flying light aircraft, we use headsets which include ear protection from the noise of the fan. Being that unpowered gliders are presumably much quieter, are the same headsets used?
My assumption is that gliders are radio equipped, and pilots are still talking to ATC or their airfield traffic information. If this is not the case, are headsets still used for intra-cockpit communications or are they really quiet enough to talk normally?

I have never seen any glider pilot with a headset (unless it is a motor glider, and then only on TMGs, which are basically normal light aircraft with longer wings). The noise in the cockpit stems only from the airflow, and at cruise speeds around 100km/h, you don't have any problems. Think about the noise in a car at motorway speeds.

@Monolo so at a busy airfield with other GA traffic, surely they must still be at very least monitoring the radio for traffic? Wouldnt they use the same circuit for landing?

Oh, yes they do monitor the frequency, they just don't need a headset - the loudspeakers in the cockpit are sufficient for that. Remember, the noise is no more than what you experience in a car. Whether they use the same circuit depends. In some cases the powered planes use one circuit (e.g., the right-hand one) and the gliders the other (the left-hand one, in this example).

Not all gliders are radio equipped (at least in the UK), especially older Annex 2 gliders

Headsets are not "required" for any aircraft, powered or not.  Headset use is a personal preference which has become more popular in recent years. I learned to fly in the 1970's and we only used the aircraft speaker and lots of yelling. Later I flew a Cessna 414 that had a boom mic attached to the aircraft for hands free, without a headset.

No, but a hat to protect the head from the sun. You may call this the glider pilot's headset ;-)

Glider pilot with hat (picture source)
The flight noise is just a faint hissing sound, and the most noise is either produced by the electrical variometer or the radio. On a busy day and with everyone on the same frequency, I often switched the radio silent when high up. When you receive transmissions from tens of kilometers away, you often receive parallel transmissions, which result in a very loud and annoying crackling in the radio.

So, what a handheld mic and cockpit speakers then?

@Jamiec Cockpit speakers and a gooseneck microphone or even better a panel mount microphone (e.g. http://shop.segelflugbedarf24.de/Flugzeugausstattung/Funkgeraete/Zubehoer-fuer-Funkgeraete/Einbaumikrofon::1177.html). Gliders are really quiet and you don't have to be kissing your micro, 0.5m between your face and the panel microphone are enough.

In the UK, I've never known a headset used except in motorgliders.  Apart from being unecessary, you want to hear the vario and more importantly the airflow (it will generally go quiet close to the stall).
I've flown gliders that don't even have radios on board, where a hand held is used, where there is a fitted radio with handheld mic, and fitted radio with bendy mic thing and a button on the stick.  The last is the most useful - I've been asked to call final at a towered airfield before and heldhelds aren't good for that (with one hand on the stick and the other on the airbrake) - without a third hand you have to call early on base.
I'd concur with Peter that the narrow-brimmed hat is standard equipment.  In some ways its probably a more important piece of safety gear than the parachute! :)


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What were the L/D ratio of the A-90 Orlyonok at its different operational atlitudes?
The A-90 Orlyonok was designed to operate in ground effect (altitude significantly lower than its wingspan). If I understand correctly, when in ground effect, the L/D ratio is better due to induced drag being lower. Thus, I imagine the L/D ratio of the A-90 is high when cruising near at low altitude, but I failed to find any figure *. Moreover, according to Wikipedia, this aircraft have a ceiling of 3000m (not really in ground effect).
I'm interested in the performance differences between flying at ground effect altitude and at almost 10000ft AGL.
What were the L/D ratio of the A-90 Orlyonok at its different operating altitudes (when in ground effect, at its ceiling, and at any other altitude it would spend time flying at)?

* I only find a paper that states GEV in general have a L/D ratio of 23 without saying if it applies to the A-90 nor at what altitude this L/D ratio is found

As I read it, the 23:1 L/D value is for the Lippisch X-112. Of course there cannot be just one value, especially without giving a height at which this value applies.